In the old days it was graffiti on the white board. But due to the rise of networking websites such as MySpace and Facebook, university tutors are finding themselves the subject of high-tech harassment.

Some 41 institutions in the UK have signed up to Facebook. Since its launch in February 2004, it has attracted 7.5m members and an estimated 90% of students at participating universities are active users.

Its success lies in presenting a forum in which everyone at a university can create a personal profile, send messages, and share photos. But these very qualities of ease-of-use and campus-wide membership are making it the prime place to abuse staff.

"The problem is that the site institutionalises gossip," says Dr Helen Smith, a tutor at the University of York. "It makes permanent all the things that usually people would chat about in the pub." Her antipathy towards the site started when one of her students left a series of unpleasant remarks about the university's lecturers. "I was so angry I haven't looked at the site since. I don't want to find out someone has written something negative about me, and put myself through all that upset."

In particular, the discussion boards of Facebook's many "groups" provide an unregulated platform for disgruntled students to publish whatever they like. While the majority of such groups may be harmless, such as 'The Anti-Dan Brown Coalition' (York) or 'Avocado Aficionados' (Oxford), there are plenty that aren't. Type "hate" into Facebook's internal search engine and you get over 500 results.

Significantly, while Facebook is mainly used by students, anyone with an academic login can sign up. An increasing proportion of university staff are joining the service - either as active participants or, more commonly, through fear or curiosity about what their students are saying.

For Dr Henry Bennet-Clark, of Oxford University, the decision to join was not even his own. He first discovered that he had a Facebook profile when it was picked up by the student newspaper Cherwell. The fake profile, which claimed he'd been a member of the Hitler Youth, was the creation of a second-year computer science student. "I, personally, was rather careful to do nothing," says Bennet-Clark, "but we had some crisp words with the perpetrator and he was summarily disconnected for the rest of that term."

Bennet-Clark is worried about the growing potential for online abuse of this sort, but says that in a close-knit Oxford college, "unpleasant bloggers and practical jokers seem unable to keep quiet, so the word gets round remarkably quickly". In larger academic communities, however, the problem is more complex. Although Facebook does have the facility to report unpleasant comments, no university has the resources to patrol its hundreds, if not thousands, of pages.

Another university tutor, who asked not to be named, says although the majority of the material is humorous, some is deliberately hurtful. "Facebook seems so trivial and stupid," she says, "because it's full of things like 'Oh god I have a hangover.' But it also throws up these comments about tutors - which are very painful."

There's also the issue of Facebook's operation as an informal feedback circuit having an impact upon teaching performance. "It becomes very personal," she explains. "You worry that they'll rate you as the least attractive tutor ever; what you should be worrying about is whether or not you're doing a good job."

When it comes to what students really think about their tutors, too much knowledge is a dangerous thing. "It makes tutors uncomfortable. You might start thinking 'I'd better not say anything bad about this student because they're big in Facebook and it might end up on the web.'" Sally Hunt, joint general secretary of the University and College Union, says: "Online gossip might seem harmless enough, but it can lead to online bullying and malicious rumours. If students have real concerns about their lecturers, they need to go through the proper channels, rather than posting on a website."

Sadly, however, this problem is likely to become more common. In the US, where social networks like MySpace and Facebook have been around for longer, there is a growing catalogue of unpleasant activity. In April 2005, three students at the University of Mississippi were threatened with legal action after making derogatory comments about a female tutor.

Students at six other American universities have been disciplined following investigations of material posted on networking sites. But while US institutions are producing specific strategies to educate staff and students, the majority of UK universities have not yet formed a coherent response. "I'm sorry, Fate-book?" was a typical response from universities contacted. "Is it a chat show?" Although most campuses already have general internet-usage guidelines, these are quite unprepared for the present situation, where the vast majority of students join a single site.

Fred Stutzman, at the University of North Carolina, has been studying the social mechanics of Facebook networks for over a year. He thinks that the problem is less to do with the website, and more with student attitudes. "Students have grown up being comfortable with technology," he says. "They've spent their lives online. So they're comfortable with this, and they aren't aware of the dangers."

So what, then, should UK higher education institutions be doing? Firstly, forget trying to ban Facebook, says Stutzman. "They have to figure out rules for how the culture wants to use the service, and give their students good information about its context, not try to scare them."

Universities need to take steps to educate their students, so that everyone who writes a message on the 'I Hate Dr Jones's Guts' discussion group knows their comments are both public and lasting. "Students don't realise that once you've said something on the internet, it's permanent," says Stutzman. "There's this weird expectation that when they're putting stuff out there, it's only being looked at by a few people. And as a result, students really do let their guard down."

As the comments left illustrate, serious work is required before UK students become aware of the inadvertent - and potentially extremely hurtful - consequences of their online activity, or begin to appreciate that what they write across Facebook's pages is on public display.

"It's ethically murky, isn't it?" agrees another tutor. "Students don't think. They would all be flabbergasted if they knew we were reading what they were writing."